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Using PMOD RTCC with PetaLinux 2017.4 on Arty Z7



Is there anyone with information (better yet a working example) on how to get the PMOD RTCC working with the 2017.4 version of PetaLinux.  I am using the unmodified PetaLinux release from Digilent for the Arty Z7 -20 but the OS does not seem to recognize the RTC device.  I do see a message similar to "/dev/misc/rtc not found" go by on boot.  I don't want to hack around if it is just a straightforward setting to make things work.  I will be most grateful for any help.

Thanks, Tom

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Hi @troden,

"/dev/misc/rtc"  is the place where RTCs will be instantiated once the RTC driver has been called and applied, for many embedded processors this is either part of their architecture or there is a explicit RTC IC on the board for them whit the driver in the kernel module. Unfortunately this not the case with the Pmod RTCC, this one is an external RTC .

You first need to either add the  PmodRTCC IP or the AXI I2C IP to your hardware design, then you need to update the dts to include the IP and finally, before building the kernel, you need to include the xilinx I2C driver (and optionally if you managed to adapt the mcp7941x linux driver to work with the xilinx i2c driver include that one as well) after building the kernel you can start accessing the RTC in "/dev/misc/rtc"  if the mcp7941x linux driver works otherwise it will be a generic I2C device.

Here is a link on how to use the xilinx I2C driver.

Here is a link on the mcp7941x linux driver discussion on a separate forum.

- Ciprian

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